Diagnostics

Winds of change

A new kind of breathalyser

JUST over 50 years ago Robert Borkenstein, then a little-known forensic scientist, invented the breathalyser, allowing instant analysis of alcohol levels in the blood from a sample of breath. It turns out, though, that a person's breath may reveal a great deal more about him than simply whether or not he is fit to drive. It could also help doctors diagnose illnesses.

Every breath that is exhaled contains trace amounts of at least 1,000 compounds. Yet mass spectrometry, electronic noses and the other ways of detecting these compounds tend to be too slow or too imprecise. Mass spectrometry, for example, can have difficulty identifying a single component from within a mixture of many molecules.

Michael Thorpe and his colleagues at the National Institute of Standards and Technology, and the University of Colorado, both in Boulder, have been looking for something better. This month in an online journal called Optics Express, they demonstrate a technique that may simultaneously—and quickly—identify tiny amounts of many different substances in the breath.

They use something called an optical “frequency comb”, which is a precise tool for measuring different frequencies of light—made possible by advances in ultra-fast lasers. The frequency comb is generated by a laser that produces a series of very short, equally spaced pulses of light (like the teeth of a comb) across a broad spectrum of frequencies.

The team “combed” breath samples from volunteers with the light pulses. Each molecule has its own light-absorption spectrum, so by analysing which colours of light were absorbed, and in what amounts, the team could work out which chemicals were present and in what concentrations. The breath of one student smoker, for example, contained a level of carbon monoxide five times greater than the breath of the non-smokers.

Some diseases and conditions can cause small changes to the breath. Excess methylamine can, for example, signal liver and kidney disease. Ammonia may be a sign of renal failure and elevated acetone levels can indicate diabetes. Nitric oxide is a sign of asthma and other lung diseases, such as chronic obstructive pulmonary disease, cystic fibrosis and bronchiectasis (the abnormal widening of airways). However, simultaneously monitoring nitric oxide, carbon monoxide, hydro-peroxides, nitrites, nitrates, pentane and ethane in the breath, would allow a much more definitive diagnosis of asthma.

The technique is a long way from the doctor's surgery—it has not yet been through clinical trials. But as a new kind of breathalyser, more selective and sensitive than any existing device, it promises to become a fast, cheap screening tool. In addition, lots more markers of disease in the breath no doubt remain to be discovered.

What the researchers delicately forget to mention is that the breath is not the only source of biological aromas suitable for chemical analysis. Perhaps not what Borkenstein had in mind when he created the breathalyser, but another way of sniffing out the truth.